In some fluid ejection devices, a flow path including a fluid pumping chamber and a nozzle can be formed in a substrate. Fluid droplets can be ejected from the nozzle onto a medium, such as in a printing operation. The fluid pumping chamber can be actuated by a transducer, such as a thermal or piezoelectric actuator, and when actuated, the fluid pumping chamber can cause ejection of a fluid droplet through the nozzle. The medium can be moved relative to the fluid ejection device, e.g., in a media scan direction. The ejection of the fluid droplet can be timed with the movement of the medium to place a fluid droplet at a desired location on the medium. A fluid ejection device typically includes multiple nozzles, such as a line or an array of nozzles with a corresponding array of fluid paths and associated actuators, and droplet ejection from each nozzle can be independently controlled by one or more controllers. In some cases, at least a portion of any un-ejected fluid can be re-circulated to remove air bubbles, aerated ink, debris, and other contaminants from the substrate.